Q: A few years ago, I used Yapta, which tracks airfares and alerts you when the price of your flight has gone down after purchase so that you can apply for a "fare drop" flight credit on a future flight. It worked very well. But like many things I forgot about it. Anyway I found it again this morning and downloaded the application to my iPad and iPhone and tried to put my first flight in. I got as far as flight number when it crashed and I started over again … three times. Since the app hasn't been updated since 2011 I wonder if it still works? Or if you have any suggestions for other sites that do the same thing. It would be great if such a service existed for flights, car and hotel rooms!

A: Yapta does indeed work well when a fare goes down after you buy it, as long as you've booked on a participating airline. It only works with nine airlines, however (soon, it will only work with seven airlines, once AirTran is fully integrated with Southwest, which doesn't participate, and when the almost-inevitable American/ US Airways merger takes place). JetBlue, Airtran and Alaska will offer a voucher or electronic credit, good for future travel up to a year, on any price drop, without deducting a fee from the refund. Virgin America deducts a $75 change fee; Hawaiian a $100 fee, and American, Delta, United and US Airways a $150 fee, on domestic flights (fees are as high as $250 on international flights, which often wipes out any savings). And there are all kinds of loopholes. For example, as Yapta states in the "airline policies" page, American reserves the right to decline refunds "when reduced fares are for sale for a limited period of time," whatever that means.

Another option for airfares as well as hotel rooms is Orbitz.com's "Price Assurance" program. If you book an airfare or a hotel room, and another Orbitz customer books the exact same flight or a room in the same category at the same hotel for the same travel dates at a lower price before your trip commences, you'll get a check for the difference between what you paid and the other customer paid. Orbitz claims that it has issued more than $10 million in refunds under this arrangement. Yet another possibility for hotels is Tingo.com. Tingo only works with hotel rooms, and the major difference is that another Tingo customer does not have to book the same hotel stay (room type, exact in and out dates) for a refund to kick in. If any night of your stay has been reduced by the hotel before you arrive, Tingo automatically refunds your credit card. Or, if a better room becomes available at the same price it will offer to upgrade you for the price of the less desirable room. Tingo is relatively new, but it has so far issued more than $250,000 in refunds.

I don't know of a service that works the same way for rental cars.

If the Yapta.com app isn't working, I'm pretty sure the website itself is still fully functional, so perhaps you should just use your laptop or home computer.

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George Hobica is founder of the low-airfare listing site Airfarewatchdog.com.

Have a question about air travel? Send it to ask@airfarewatchdog.com. Questions can only be answered in this column and not individually.

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